The present invention relates to the use of heat from geothermal fluids, including steam and brines, and is particularly concerned with the use of waste heat (i.e., heat contained in brine or steam which would normally be discarded, e.g., reinjected, as waste) from geothermal brine or steam obtained from geothermal energy power generation, for the manufacture of chemicals, particularly alcohol, by such processes as hydrolysis, fermentation and distillation. The geothermal source can be naturally occurring, or man made (as by atomic explosion underground and/or by injection of water or other heat exchange fluid into a deep well and/or by injection of a heat exchange fluid, e.g., water, into a spent shale retort).
Various methods are known for utilizing the geothermal steam or brine for electrical power generation. Thus, according to one procedure, the hot geothermal brine is directly flashed and the resulting flashed steam is then expanded through a turbine for electrical generation. According to another mode of procedure, a tube and shell heat exchange apparatus is employed for indirect heat exchange contact between the hot brine on one side and water or a working fluid on the other side, and the heated steam or working fluid is then passed to the turbine for generating power. Such methods are described for example, in Geothermal Energy Utililization by Edward F. Wahl, John Wiley & Sons, New York (1977).
According to a third method, direct contact heat exchange is provided between the geothermal brine and an immiscible (e.g., isobutane) working fluid, and the working fluid is expended through a turbine to produce electrical energy. Illustrations of the latter system are those disclosed in U.S. Pat. No. 3,988,895 to Sheinbaum, application Ser. No. 589,068, filed June 23, 1975 by S. F. Woinsky, application Ser. No. 873,264 of E. F. Wahl, et al, filed Jan. 30, 1978, and application Ser. No. 50,868, of P. Sadkukhan, filed June 21, 1979 (all of which are incorporated herein).
In all three of the above systems and processes, waste brine and/or steam (which still contains a substantial amount of heat) is obtained following electric power generation, and such waste brine or steam is usually at too low a temperature for economical energy conversion in large amounts.
It is well known to employ waste or exhaust steam from a power generating turbine for heating a distillation plant or evaporator. See, for example, U.S. Pat. Nos. 3,412,558; 3,243,359; and 3,451,220.
The object of the present invention is to utilize waste heat in the form of waste brine and/or exhaust steam from a power generating turbine powered by geothermal energy, in a novel manner for producing valuable chemicals. Thus, for example, substantially anhydrous liquid alcohols are high grade fuels or can be used as high grade fuels. Gasoline with about 10% ethanol is called gasohol. Fermentation of sugar or starch can be used to transform the sugar or starch to ethyl alcohol and carbon dioxide. Industrial alcohol can be made from agricultural wastes by first digesting the waste to sugars and fermenting the sugars to form dilute ethyl alcohol, then distilling the dilute alcohol to obtain concentrated alcohol, that is at least about 90%, typically 95% alcohol. However, heat is required for carrying out digestion (including enzymatic acid or base catalyzed hydrolysis, as hydrolysis of starch or cellulose), fermentation, and distillation operations.